<!DOCTYPE html>
<html>
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style>
		div {
			width: 300px;
			height: 200px;
			background-color: red;
		}

		.test3 {
			/*margin-top: 20px;*/
			/*border-top: 1px solid #000;*/
			/*padding-top: 1px;*/
			padding-top: 10px;
		}

		.test4 {
			background-color: green;
			/*margin-top: 10px;*/
		}

		/*.test1 {
			margin-bottom: 20px;
		}

		.test2 {
			background-color: green;
			margin-top: 10px;
		}*/
	</style>
</head>
<body>

	<div class="test3">
		<div class="test4"></div>
	</div>

	<!-- <div class="test1">
		
	</div>

	<div class="test2">
		
	</div> -->
	
</body>
</html>